命名管道 - write() 和 read() 问题
我正在 LINUX 下使用 C++ 进行编程。 我有两个独立的进程。我应该使用命名管道提供通信。
读者： - 使用 mkfifo 创建 FIFO - status = mkfifo(myFIFO, 0666) - 使用 open 打开管道 - fifo = open (myFIFO,O_RDONLY) -从管道读取 - num = read(fifo, temp, sizeof(temp))
编写者： - 打开管道 - fifo = open(myFIFO, O_WRONLY); -写入管道 - num = write(fifo, string, strlen(string));
我注意到文件描述符返回用于读取过程 和 write process 都是 0。另外，在命令 write 之后，我可以在终端上看到应该写入管道的字符串。我不知道为什么它显示在终端上...另外，写入的字节数是 0...
请帮帮我吗？ 谢谢你！！！
// read.cpp:
#define myFIFO "/temp/FIFO"
int main(){
int num, fifo, status;
char temp[32];
if (status = mkfifo(myFIFO, 0666) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (fifo = open(myFIFO, O_RDONLY) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (num= read(fifo, temp, sizeof(temp)) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
printf("In FIFO is %s \n", temp);
}
在另一个文件中：
// write.cpp:
#define myFIFO "/temp/FIFO"
int main() {
int status, num, fifo;
char string[]="Testing...";
if (fifo = open(myFIFO, O_WRONLY) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (num= write(fifo, string, strlen(string)) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
}
I am doing programming in C++, under LINUX.
I have two independent processes. I should provide communication using named pipe.
Reader:
-creates FIFO using mkfifo - status = mkfifo(myFIFO, 0666)
-opens the pipe using open - fifo = open (myFIFO,O_RDONLY)
-reads from the pipe - num = read(fifo, temp, sizeof(temp))
Writer:
-opens pipe - fifo = open(myFIFO, O_WRONLY);
-writes to the pipe - num = write(fifo, string, strlen(string));
I have noticed that the file descriptor returned for read process
and write process are 0. Also, after command write, I can see on my terminal, the string which should be written to the pipe. I don't know why it is shown on terminal... Also, the number of bytes that are written is 0...
Would you please help me?
Thank you!!!
// read.cpp:
#define myFIFO "/temp/FIFO"
int main(){
int num, fifo, status;
char temp[32];
if (status = mkfifo(myFIFO, 0666) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (fifo = open(myFIFO, O_RDONLY) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (num= read(fifo, temp, sizeof(temp)) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
printf("In FIFO is %s \n", temp);
}
And in another file:
// write.cpp:
#define myFIFO "/temp/FIFO"
int main() {
int status, num, fifo;
char string[]="Testing...";
if (fifo = open(myFIFO, O_WRONLY) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (num= write(fifo, string, strlen(string)) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
}
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评论（2）
您的代码中基本上至少有四个错误。创建 FIFO 时，必须使用“open”调用返回的文件描述符。但是，您将其与 0 进行比较，并将比较结果分配给用于保存文件描述符的变量：
正确的代码应该如下所示：
或者像这样，如果您坚持保存一行代码：
并且与阅读完全相同的故事：
正确的代码：
在写入 FIFO 的代码中存在完全相同的两个错误。
You basically have at least four errors in your code. When you create a FIFO, you have to use a file descriptor returned by "open" call. However, you are comparing it with 0 and assigning a result of a comparison to a variable that was meant to hold a file descriptor:
The correct code should look like this:
Or like this, if you insist of saving one line of code:
And exactly the same story with reading:
Correct code:
In your code that writes to FIFO there exactly the same two errors.
问题出在您的代码中：
fifo = open(myFIFO, O_WRONLY) < 0的计算结果为fifo = (open(myFIFO, O_WRONLY) < 0)。您得到零，因为open()返回的值是>= 0。The problem is in your code:
fifo = open(myFIFO, O_WRONLY) < 0evaluates asfifo = (open(myFIFO, O_WRONLY) < 0). You get zero because the valueopen()returns is>= 0.